Advice please? What is this?

[LuckyCornish13]

My 3 year old has spent last night and today with my ex. I was just doing his nappy and putting him in his PJs when I noticed this mark, and I don't have a clue what it is? It's a tiny bit raised. Am I overlooking something really obvious as to what this could be? My son seems his normal, chatty self and has made no remark as to it being sore... Advice or suggestions please?

[Spinaroo]

Could he have leaned against a radiator and burned it without a nappy on? I know someone whose baby put their hands on a very hot radiator and was burned.

[Spinaroo]

Also what was he doing just before- did he have something in his pocket maybe and was leaning on it. Have another look in 10 mins - if it has diminished it will likely be this

[SomethingFunny]

Looks like what my sons skin looks like after he has worn a plaster - the right shape, colour and slightly raised (but no discomfort).

[Optimistletoe1]

Looks to me as though a nappy fastening didn't get done properly and the sticky bit stuck to his skin. (I'm not entirely sure what part of his anatomy you're showing in the photo).

[LuckyCornish13]

Thanks Spinaroo! Highly unlikely re the radiators as ex hates him being without nappy/pants on, plus they have underfloor heating and a fire, no actual radiators. Just checked his jeans and no pockets lol.
I found it within 10 minutes of him being home as our Sunday afternoon tradition is to cuddles up in our PJs, so really not sure what it is. I'm debating ringing the ex as I don't want him to think I'm accusing him (he's a very under confident daddy) but really bugging me what the mark is!

[LuckyCornish13]

It's his bum cheek

[cate16]

Has he had any new clothes? If so could the sticky size label have got stuck to him? This happened to me the other day- I went to get in the bath and found a size sticker on my back!
Another thing is - has he been wrapping presents? Sellotape stuck to him.

[Littlef00t]

I'd say a sticker or plaster?

[Haggisfish]

Does look like a plaster. Maybe see if it fades within an hour or do-could just be car seat belt digging in.

[thatsn0tmyname]

I'd say it's an irritation to adhesive in a plaster or nappy tab.